The objectives of the proposed research are to explore the influence of various aspects of the rat pup stimulus complex (contact: tactile, thermal, taste; exteroceptive: sight, sound, smell) on the induction (in virgins), initiation and maintenance (postpartum or post-Cesarian-section delivery) of maternal behavior. The sensory regulation of prolactin secretion in lactating, thelectomized (nipple-removed) postpartum, and maternal virgins will also be assessed. Finally, experiential, social, and maturational influences on maternal responsiveness will be studied. We have found that prolactin is released in response to pup contact in the absence of suckling; this release is enhanced by a previous lactation experience or by a greater than 7 day duration of the maternal behavior state in virgins. We will pursue the roles of pup age, exteroceptive pup stimuli (e.g. ultrasounds), gender, maternal behavior and lactation experience in enhancing prolactin secretion. Time-lapse videotape recordings will be used to assess the ontogeny and maintenance of maternal behavior in various subjects, i.e., weanlings, adult males, adult females induced to be maternal with or without hormonal stimulation. Experiential (age of weaning, rearing with or without littermates) and maturational (body weight, forebrain inhibitory mechanisms) influences on changes in maternal responsiveness with aging will be studied.